This invention relates to an annular elastic track for use in vehicles for civil engineering, construction works and agricultural works.
Molded rubber tracks are in many cases being substituted for conventional metal tracks. Rubber tracks offer better maneuverability, better ride quality in rough fields, better flotation in wet areas, improved side hill stability, excellent traction, low maintenance and versatility compared to steel tracks.
Additionally, rubber tracks are replacing conventional rubber tires on tractor and other agricultural vehicles such as combines, trenchers, snow removers, spreaders, sprayers, wagons and carts, since rubber tracks are more friendly to agricultural fields, offer better flotation and less compaction than rubber tires, resulting in better crop yield. The use of rubber tractor tracks permits farmers to get in and out of fields earlier in the planting season and plant more crops as compared to rubber tire-equipped agricultural vehicles.
In civil engineering applications tracks are employed on many construction equipment type vehicles such as road pavers and the like. These tracks are generally made from steel or steel with urethane or rubber pads. These tracks require much maintenance and in the case of steel tracks the damage to paved surfaces is a serious problem. Also, these construction type tracks can be placed over pneumatic tires for skid steer equipment. A new advance in this area is the use of an all rubber steel cord track. The Goodyear Tire and Rubber Company provides such a track under the trademark TRACKMAN(copyright), and the Bridgestone/Firestone Company provides a similar track under the name Firetrax(copyright). These tracks have rubber lugs that extend across the entire width of the track. Each has swept back axially outer portions, which limits the amount of lateral extending edges. These tracks are good on paved surfaces, but are deficient in applications that have wet soil or loose sand and gravel. Additionally, the swept back outer ends create bending stresses on the underlying belt structure as the track bends over the wheels.
Rubber tracks are defined by an endless rubber belt reinforced with continuous flexible steel cables bonded into the rubber. Presently, a complete rubber track is molded flat in multiple sections, which are sequentially then bonded together during the curing process. Alternatively an endless rubber track can be made in annular form wherein the track is made from an uncured belt and a plurality of drive lugs wherein the drive lugs are urged into cavities formed in inner segments of a molding press, partially final formed and pressed onto the inner periphery of the belt, the belts and drive lugs are positioned in the molding press to be cured and molded together while treads are formed on the outer periphery of the belt. The drive lugs are finally formed and the completed belt is cooled and removed from the molding press forming an annular track as described in U.S. Pat. No. 6,051,178 issued Apr. 18, 2000, to the assignee, The Goodyear Tire and Rubber Company.
In each of the methods of manufacture the outer periphery has a plurality of spaced tread lugs. Generally in the prior farm tire art these tread lugs extend from each lateral edge of the track towards the center of the track terminating at the central location or mid-point of the track. These lugs generally take the appearance of agricultural tire lugs with a generally inclined but slightly more transverse extending inclination relative to the direction of travel. Lugs of this design have inherently experienced high wear patterns in the central location of the track. Additionally, these lugs have been staggered or are circumferentially off-set from one side of the track to the other. This helps insure that the track has sufficient bending moment as the track traverses over the drive wheels and guide wheels at each extremity of the elliptical shape track as it traverses in use. If the tread lugs extend from one side of the tracks lateral edge to the opposite side, then it is believed that the lugs must be perpendicular to the direction of the circumferential links of the track in order for the lugs to achieve appropriate bending moment in flexibility as it rotates around the drive wheels. For this reason, it is felt necessary to provide the tracks with two sets of lugs that act somewhat independently relative to the lugs set of the opposite side of the track so that the track itself can bend in a rather flexible nature. Absent this bending severe loads result in the belt reinforcing structure causing potential separations and other defects in the track itself as has been observed in some of the prior art rubber construction tracks previously mentioned.
It is an object of the present invention to provide a new directional tread pattern that can extend from one lateral side of the track to the opposite lateral side of the track in a continuous tread lug without adversely affecting the bending capability of the track as it traverses around the drive wheels. Another objective is to provide improved soil discharge at the lateral extremes of the track while increasing the wear properties of the track lugs based on its unique design.
A directional annular elastic track has guide lugs on the inner circumference and rubber tread lugs on the outer circumference and a thin band continuously extending in the circumferential direction. The thin band is circumferentially reinforced by substantially inextensible cords or bands. Preferably the cords or bands are steel reinforced materials.
The track has a plurality of spaced rubber tread lugs. Each rubber tread lug has a first lateral end portion, a middle portion and a second lateral end portion. Each portion is oriented perpendicular to the circumferential direction wherein the middle portion is projected forward relative to the lateral portions.
Each rubber tread lug is separated by a groove. The groove extends completely across the track and has a groove width (WM) between the middle portions of adjacent lugs and a groove width (WL) between the first and second lateral end portions of adjacent lugs. The groove width (WM) is less than (WL). Preferably the groove width (WM) is 75% or less than the lateral groove width (WL).
When one extends a plane perpendicular to the track circumferential length such that it lies within each groove and is centered in the groove between adjacent middle portions, the plane (PL) intersects at most one groove wall in each of the lateral end portions of the tread lugs. The lugs have a radially outer tread surface located between a leading edge and a trailing edge. The leading edge and trailing edge are parallel over a majority of the lug length and in the middle portion protrudes toward the forward direction of travel of the track. The leading edge adjacent the middle portion extends at an amplitude (AL) from the leading edge adjacent the lateral ends. The trailing edge adjacent the middle portion extends at an amplitude (AT) relative to the trailing edges adjacent the lateral end portions. (AL) is 125% or more than (AT) as measured relative to the corresponding edges of the lateral end portions. As described above it is preferred that each of the lateral end portions is circumferentially aligned relative to the tracks direction of travel.
It is preferred that the lugs have a total lug length (L) and the middle portion has a length at least 50% of (L). In the preferred embodiment each lug lateral end portion has an outer chamfered lug wall extending in the circumferential direction.